"""Example of the Observer pattern using Pyro.
Copyright 2010 Allen B. Downey
License: GNU GPLv3 http://www.gnu.org/licenses/gpl.html
"""
from copy import copy
# this import has to be here in case we get a Pyro error from an RMI
import Pyro.errors
from remote_object import RemoteObject, NameServer
class Subject(RemoteObject):
"""A Subject is an object that keeps track of the Observers
watching it. When the state of a subject changes, it
notifies each Observer on the list."""
def __init__(self, name):
RemoteObject.__init__(self, name)
self.observers = []
def notify_observers(self):
"""notify all registered observers when the state of
the subject changes"""
for observer in copy(self.observers):
try:
print 'Notifying', observer
ns = NameServer()
proxy = ns.get_proxy(observer)
proxy.notify()
except Exception, x:
# this clause should catch errors that occur
# in the Observer code.
print ''.join(Pyro.util.getPyroTraceback(x))
except:
# this clause should catch Pyro NamingErrors,
# which occur when an observer dies.
print 'Removing ' + observer
self.observers.remove(observer)
# the following methods are intended to be invoked remotely
def register(self, name):
"""Registers a new Observer (invoked by the Observer)."""
self.observers.append(name)
print 'Registered ' + name
class SimpleSubject(Subject):
def __init__(self, name, state=0):
"""The state of a SimpleSubject is a single integer named 'state'
In a real application, the state would be a more elaborate
data structure."""
Subject.__init__(self, name)
self.state = 0
# the following methods are intended to be invoked remotely
def set_state(self, state):
"""Changes the state of the Subject."""
print 'New state', state
self.state = state
self.notify_observers()
def get_state(self):
"""Gets the current state of the Subject."""
return self.state
sub = SimpleSubject('simple_subject')
sub.requestLoop()